JPH06100895A - Process for cleaning plastic bumper - Google Patents

Abstract

PURPOSE:To realize the cleaning in a short process without using any organic solvent for cleaning, before coating, a plastic bumper molded particularly by using zinc stearate as an internal mold release agent. CONSTITUTION:This process comprises the steps of: cleaning a polypropylene and/or polyurethane bumper at 60-80 deg.C with an acidic aqueous cleaning solution which has a pH of 2 to 4 and contains a mineral acid in an amount of 0.1-100g/l, a fluorine compound in an amount of 0.01-10g/l, a nonionic surfactant with an HLB of 12 to 16 in an amount of 0.1-10g/l, a polyethylene polypropylene derivative foam inhibitor with an HLB of 6 or lower in an amount sufficient to provide a weight ratio of this foam inhibitor to the nonionic surfactant of (0.1 to 2):1, and a sodium and/or ammonium pH regulator; washing the cleaning solution with water and blowing it away by air; and drying at room temperature to 80 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-painting cleaning method performed as a pre-treatment when painting a plastic bumper part constituting an automobile body. The present invention relates to a method capable of dealing with cleaning of two kinds of composites in a short process and one step.

[0002]

2. Description of the Related Art Conventional cleaning agents for various plastic bumper parts include 1,1,1-trichloroethane, 1,
Halogenated hydrocarbon solvents such as 1,2-trichlorotrifluoroethane have been used.

However, the halogenated hydrocarbon solvent has a good detergency, but on the other hand, its use is limited due to its effect on the environment. Nowadays, the amount of its use is reduced in the entire industry. In addition, the solvent replacing the halogenated hydrocarbon still has the problem of the influence on the human body from the use environment and the problem of fire, and the development of new cleaning agents to replace these is underway.

As an alternative to the above-mentioned detergent, a detergent using an aqueous solution containing alkali such as sodium hydroxide and potassium hydroxide and / or phosphoric acid and acid such as phosphate and carbonate is disclosed in JP-A-2-55599. In No. 5, there is described a cleaning composition in which an alkali or phosphoric acid mainly containing a potassium salt and an acid mainly containing a phosphate, a polyethylene glycol type nonionic surfactant (HLB12 to 18) and an antifoaming agent are mixed. Has been done. In addition, JP-A-4-27
No. 472 includes an alkali cleaning solution containing an alkali builder (sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, etc.) and a surfactant, an organic acid (malic acid, lactic acid, citric acid, tartaric acid, etc.) and an inorganic substance. A cleaning method is described in which two-step cleaning is performed using an acidic aqueous solution containing an acid (sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc.).

However, it is difficult to obtain sufficiently good detergency when using the aqueous solution detergent described in the above publication, and particularly when different types of plastics are washed in the same step, a solvent There are problems such as needing help, a two-step cleaning of cleaning with an acid aqueous solution after cleaning with an alkaline aqueous solution, and a complicated cleaning process.

Also, when coating a plastic bumper molded product, what is an obstacle is a mold release agent (external mold release agent) used at the time of molding, and a mold release agent mixed with the plastic material itself (internal mold release agent). There are contaminants and the like that adhere during the process from the molding process to the painting process.

First, there are various releasing agents (external releasing agents) used at the time of molding, including paraffin type releasing agents.
Conventional halogenated hydrocarbon solvents were easy to dissolve and clean, but when using a cleaning agent with the above aqueous solution, it is difficult to completely remove the external release agent, which adversely affects the finish and adhesion of the coating. There was a problem such as giving.

As the above internal release agent, a stearate salt, especially zinc stearate is generally used in many cases. However, washing with an alkaline aqueous solution does not allow the internal release agent to be sufficiently removed. Are likely to remain, resulting in defects such as poor finish during coating (generation of pinholes) and swelling (blister) of the coating film due to deterioration of water resistance.

Further, contaminants attached from the outside are often solved by a general washing method, but in order to prevent redeposition, it is necessary to stabilize the dispersion in the washing liquid.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to use a non-solvent type cleaning agent for cleaning plastic bumpers prior to coating without using a solvent, that is, a single-step cleaning with a short cleaning step. It is an object of the present invention to provide a method for cleaning a plastic bumper, which is achieved by a configuration including steps of cleaning, followed by washing with water, air blowing, and drying in that order.

Another object of the present invention is to provide a method for cleaning a plastic bumper, which is extremely effective in cleaning the external mold release agent and the internal mold release agent.

Still another object of the present invention is to provide a method for cleaning a plastic bumper with a cleaning agent which is effective for cleaning contaminants and has an excellent dispersion stabilizing function.

[0013]

Means for Solving the Problems As a result of earnest efforts for a method for cleaning a plastic bumper to achieve the above-mentioned objects, the present inventors have identified a mineral acid, a fluorine compound, a nonionic surfactant and a foam suppressor. By using a cleaning agent containing an acidic aqueous solution that is contained in a range amount and further adjusted to pH 2 to 4 by a pH adjusting agent, the cleaning power of the external release agent and internal release agent can be significantly improved, and the cleaning of contaminants can be performed. It is possible to impart an effective dispersion stabilizing function to, and further, without using an organic solvent, the washing step can be shortened, etc., and it has been found that problems existing in conventional detergents and washing methods can be solved. The present invention has been completed based on the findings.

That is, the object of the present invention is to provide a polypropylene and / or polyurethane bumper with (a) a mineral acid of 0.1 to 100 g / liter, (b) a fluorine compound of 0.01 to 10 g / liter, and (c) HLB. Is 12 to 1
6, a nonionic surfactant of 0.1 to 10 g / liter,
(D) Acidic pH 2 to 4 containing a polyethylene polypropylene derivative defoamer having an HLB of 6 or less and a mixture weight ratio to the (c) of 0.1 to 2 and (e) a sodium and / or ammonium pH adjusting agent. A step of washing with an aqueous solution cleaning agent at 60 to 80 ° C, a step of washing the acidic aqueous solution cleaning solution with water and air blowing, and room temperature to 80 ° C
This can be achieved by the method (1) for cleaning a plastic bumper, which is characterized in that the steps of drying in step 1 are sequentially performed.

Another object of the present invention is to provide a method for cleaning a plastic bumper according to the above (1), wherein the polypropylene and / or polyurethane bumper is a molded article using zinc stearate as an internal mold release agent. Can be achieved.

[0016]

The present invention will be described in detail below.

The cleaning solution for the plastic bumper according to the present invention is an acidic aqueous solution containing a mineral acid, a fluorine compound, a foam inhibitor and a nonionic surfactant and adjusted to pH 2 to 4 with a sodium and / or ammonium pH adjuster.

As the mineral acid used in the present invention, sulfuric acid,
Although common ones such as nitric acid, hydrochloric acid and phosphoric acid can be used, sulfuric acid is particularly preferable in view of the influence on the equipment and the wastewater treatment load. The amount of the mineral acid used is usually 0.1 to 100 g.
The amount is preferably 1 to 10 g / liter, and more preferably 3 to 6 g / liter for reasons such as detergency and economy. The amount of the mineral acid used is 0.1 g
If it is less than 100 liters / liter, the cleaning effect due to the use of mineral acid is not observed, while if it exceeds 100 g / liter, the cleaning effect corresponding to the amount used is not obtained and it is uneconomical.

Examples of the fluorine compound used in the present invention include hydrofluoric acid and hydrosilicofluoric acid. The amount of the fluorine compound used is 0.01 to 10 g / liter, but for reasons such as detergency and economic efficiency,
It is preferably 0.2 to 2 g / liter, more preferably 0.3 to 1 g / liter. The amount used is 0.01
If it is less than g / liter, the effect due to the addition of the fluorine compound is not observed, while if it exceeds 100 g / liter, a cleaning effect commensurate with the amount used is not obtained and it is uneconomical.

These acidic components are made of polypropylene,
Effective in modifying the surface of the bumper, including the effect of modifying talc and glass fiber, which are the filler components used to modify the polyurethane bumper, and the effect of removing zinc stearate, an internal mold release agent, from the surface. At the same time, it does not cause coating defects or blister generation due to residual alkali metal generated by cleaning with an alkaline aqueous solution.

The pH of the sodium and / or ammonium pH adjuster used in the present invention is usually adjusted to 2 to 4 in consideration of equipment durability, safety and economy, but preferably 3 ~ 4, more preferably 3 to 3.5
Adjusted in the range of.

Further, as the nonionic surfactant used in the present invention, for example, polyoxyethylene laurate ester, polyoxyethylene myristate ester, polyoxyethylene palmitate ester, polyoxyethylene stearate ester, polyoxyethylene. Oleic acid ester, polyoxyethylene hydroxy autearinate ester, polyoxyethylene-9,1
0 dihydroxystearic acid ester, polyoxyethylenephenylstearic acid ester, polyoxyethylene-o-xylylstearic acid ester, etc., polyoxyethylene fatty acid ester, polyoxyethylenelaurylamine, polyoxyethylenestearylamine, etc. Polyoxyethylene sorbitan, such as polyoxyethylene alkyl amine, polyoxyethylene lauryl amide, etc., polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan oleate, etc. Fatty acid monoester, polyoxyethylene lauryl alcohol, polyoxyethylene oleyl alcohol, polyoxyethylene pine perfume alcohol Polyoxyethylene higher alcohols such as, polyoxyethylene alkylphenols such as polyoxyethylene octylphenol, polyoxyethylene octyl cresol, polyoxyethylene benzyl cresol, oleyl alcohol, polyoxyethylene octyl cresol ether, polyoxyethylene nonylphenol ether, Polyoxyethylene alkylphenol, polyethylene glycol monoureate, polyethylene glycol monooleate, polyethylene glycol stearate, polyethylene glycol sorbitan monourarate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan stearate, polyethylene glycol lauryl ether, polyethylene glycol Oleyl ether, polyethylene glycol nonylphenol ether (number of moles of added either ethylene oxide is arbitrary) can be cited. Preferred are polyoxyethylene noniphenol ether, polyoxyethylene higher alcohols, etc., in consideration of effects and safety.

Next, considering the wettability of the cleaning liquid on the material surface and the dispersion stability in the cleaning liquid for preventing reattachment of the removed contaminants, the HLB of the surfactant is usually 12 to 1.
6, preferably 12.5 to 15, more preferably 13 to
It is in the range of 15. If the HLB of the surfactant is outside the above range, the above effects cannot be sufficiently obtained. Further, the amount of the surfactant used is 0.1 to 10 g / liter, but in view of economy and wastewater treatment property, preferably 0.5 to 2 g / liter, more preferably 0.5. ~
It is 1.0 g / liter. If the amount used is less than 0.1 g / liter, the effect of the addition of the surfactant is not observed, while if it exceeds 10 g / liter, the cleaning effect commensurate with the amount used is not obtained and it is uneconomical. is there.

Next, the polyethylene polypropylene derivative foam suppressor used in the present invention includes, for example, those containing polyethylene oxide and polypropylene oxide in the structural formula, and polyoxyethylene polyoxypropylene lauryl alcohol, polyoxyethylene poly Examples include polyoxyethylene polyoxypropylene higher alcohols such as oxypropylene oleyl alcohol, Pluronic type foam suppressors, and the like. The foam suppressor is a substance for suppressing foaming during washing and foaming during washing with water, and is usually HL.
B is 6 or less, preferably 2.5 to 5.5, and more preferably 3 to 5.5. When the HLB exceeds 6, the effect of the foam suppressor cannot be sufficiently obtained, which is not preferable.

The mixing weight ratio of the surfactant to the foam suppressor is usually 1: 0.1-2, preferably 1: 0.
It is in the range of 5 to 2, more preferably 1: 1.5 to 2.

When the amount (concentration) of each of the above-described detergent compositions of the present invention is smaller than the above-mentioned amount, the desired effect cannot be sufficiently obtained, and more than the above-mentioned amount is used. If the amount is large, the plastic bumper, which is the object to be treated, will bring the cleaning liquid to the subsequent process, significantly contaminating the cleaning water, increasing the absorption of the cleaning water in the water cleaning and air blowing processes and delaying the time required for the process. It is economically unfavorable because it lowers productivity.

In the present invention, the above-mentioned acidic aqueous solution detergent is used in the treatment bath, but this concentrated solution is diluted and used as a stock solution.

As the plastic bumper which is the object to be treated according to the present invention, a polypropylene and / or polyurethane bumper can be applied.

Next, in the step of cleaning with the acidic aqueous solution cleaning agent according to the present invention, the cleaning temperature is set to a temperature close to the melting point of the mold releasing agent (external mold releasing agent) used at the time of molding in consideration of the cleaning effect. However, if the temperature is too high, there is a problem such as material deformation, and the temperature is in the vicinity of the melting point of the release agent (for example, the melting point of a paraffin wax type release agent which is generally used is about 70 to 90 ° C). ) Is usually carried out, and it is usually 60 to 80 ° C, preferably 65 to 80 ° C, and more preferably 70 to 80 ° C.

Next, in the step of rinsing the detergent with the acidic aqueous solution according to the present invention with water and air blowing, the detergent composition remaining on the surface of the bumper, which is the object to be treated, can be suitably washed with water, and then by air blowing, There is no particular limitation as long as it is possible to remove the washing water from the surface of the bumper and to prevent the intrusion of contaminants from the outside, and any conventionally used method and apparatus can be used.

Further, in the step of drying the bumper which is the object to be treated according to the present invention, the drying temperature is usually room temperature to 8
Although it is 0 ° C, it is preferably 50 to 80 ° C, more preferably 70 to 80 ° C in order to prevent the internal release agent from bleeding on the bumper surface.

[0032]

EXAMPLES Next, the present invention will be described more specifically with reference to examples.

Example 1 As a test piece, an ultra-high rigidity type of polypropylene bumper material (hereinafter also referred to as PP bumper) (without using a release agent) and a DETDA type of polyurethane bumper material (hereinafter also referred to as PU bumper) ( Two types of bumpers, zinc stearate as the internal release agent and paraffin wax type as the external release agent, were used respectively.

Next, sulfuric acid 3 g / liter, hydrofluoric acid 0.5 g / liter, nonionic surfactant (polyoxyethylene noniphenol ether ethylene oxide 10 mol adduct, HLB13.5) 1 g / liter,
The pH is adjusted to 3 by adding a pH adjusting agent (sodium hydroxide) to 0.5 g / liter of polyoxyethylene polyoxypropylene higher alcohol type foam suppressor (HLB5.5) and 1.3 g / liter of 30% ammonia water. A cleaning solution was obtained.

The above two kinds of PP bumper and PU bumper specimens were washed with the above washing liquid by spraying at 65 ° C. for 2 minutes, then washed with water and pure water, drained by air blow and dried at 75 ° C. for 7 minutes. I did.

After drying, in the PP bumper, a primer (a chlorinated polyolefin resin KX165 manufactured by Nippon Bee Chemical Co., Ltd.) was applied to a dry film thickness of 5 to 10 μm, and a top coat paint (Polyurethane resin by Nippon Bee Chemical Co., Ltd. was used. Flexene 101B326) was applied to form a coating film, which was then baked at 120 ° C. for 30 minutes to obtain a test piece having a dry film thickness of 40 to 50 μm.

Similarly, in the PU bumper, a primer (manufactured by Nippon Bee Chemical Co., Ltd., polyurethane resin type RB11
0) is applied so as to have a dry film thickness of 10 to 15 μm, and a top coat paint (manufactured by Nippon Bee Chemical Co., Ltd., polyurethane resin type flexen 101B326) is applied to form a coating film, and then baked at 120 ° C. for 30 minutes. Dry film thickness 40
A test piece having a size of ˜50 μm was obtained.

Example 2 Instead of the cleaning liquid prepared in Example 1, sulfuric acid 3 g / liter, hydrofluoric acid 0.05 g / liter, nonionic surfactant (polyoxyethylene lauryl alcohol 12 mol ethylene oxide adduct 12 mol) , HLB15) 1g
/ Liter, polyoxyethylene polyoxypropylene higher alcohol type foam suppressor (HLB5.5) 1 g / liter and 30% ammonia water 0.2 g / liter pH
The addition of a regulator (sodium hydroxide) brings the pH to 2.
PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that the cleaning liquid adjusted to 5 was used.

Example 3 Instead of the cleaning liquid prepared in Example 1, sulfuric acid 10 g / liter, hydrosilicofluoric acid 1 g / liter, nonionic surfactant (polyoxyethylene noniphenol ether ethylene oxide 20 mol adduct, HLB16)
PH to 2 g / liter, polyoxyethylene polyoxypropylene higher alcohol foam inhibitor (HLB5.0) 4 g / liter and 30% ammonia water 3 g / liter
PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that a cleaning liquid adjusted to pH 3 by adding a regulator (sodium hydroxide) was used.

Example 4 Instead of the cleaning liquid prepared in Example 1, sulfuric acid 3 g / l, hydrofluoric acid 0.5 g / l, nonionic surfactant (polyoxyethylene noniphenol ether 10 mol ethylene oxide addition) Thing, HLB13.
5) 10 g / l, polyoxyethylene polyoxypropylene higher alcohol foam inhibitor (HLB5.0) 1
PP was prepared in the same manner as in Example 1 except that a cleaning solution whose pH was adjusted to 3.5 by adding a pH adjuster (sodium hydroxide) to 1.3 g / l of 30% ammonia water and 30 g of ammonia water was used. Bumper and PU bumper test pieces were obtained.

Example 5 Instead of the cleaning liquid prepared in Example 1, hydrochloric acid 3 g / liter, hydrofluoric acid 0.5 g / liter, nonionic surfactant (polyoxyethylene noniphenol ether 10 mol ethylene oxide addition) Thing, HLB13.
5) 2 g / liter, polyoxyethylene polyoxypropylene higher alcohol-based foam inhibitor (HLB5.5) 0.
A PP bumper and a PP bumper were prepared in the same manner as in Example 1 except that a cleaning solution adjusted to pH 3 by adding a pH adjuster (sodium hydroxide) to 2 g / liter and 1.3 g / liter of 30% aqueous ammonia was used. A PU bumper test piece was obtained.

Example 6 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that the washing was performed at 60 ° C. for 2 minutes instead of at 65 ° C. for 2 minutes.

Example 7 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that washing was performed at 80 ° C. for 2 minutes instead of at 65 ° C. for 2 minutes.

Example 8 The same as Example 1 except that the cleaning solution of Example 1 was sprayed at 65 ° C. for 2 minutes instead of being sprayed at 65 ° C. for 2 minutes. Thus, PP bumper and PU bumper test pieces were obtained.

Example 9 The same as Example 1 except that the cleaning solution of Example 1 was immersed in the cleaning solution of Example 5 and washed at 80 ° C. for 2 minutes instead of being sprayed at 65 ° C. for 2 minutes. Thus, PP bumper and PU bumper test pieces were obtained.

Example 10 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that drying was performed at 60 ° C. for 7 minutes instead of drying at 75 ° C. for 7 minutes.

Example 11 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 8 except that drying was performed at 60 ° C. for 7 minutes instead of drying at 75 ° C. for 7 minutes.

Comparative Example 1 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that washing was performed at 40 ° C. for 2 minutes instead of at 65 ° C. for 2 minutes.

Comparative Example 2 10 mol of ethylene oxide adduct of polyoxyethylene noniphenol ether as a nonionic surfactant,
5 mol of ethylene oxide adduct of polyoxyethylene noniphenol ether instead of HLB13.5,
In the same manner as in Example 1 except that HLB10 was used, P
Test pieces of P bumper and PU bumper were obtained.

Comparative Example 3 PP was prepared in the same manner as in Example 1 except that drying was performed at 100 ° C. for 7 minutes instead of drying at 75 ° C. for 7 minutes.
Bumper and PU bumper test pieces were obtained.

Comparative Example 4 The pH was adjusted by adding a pH adjuster (sodium hydroxide).
Instead of adjusting the pH to 3, a PP bumper and a PU bumper test piece were obtained in the same manner as in Example 1 except that the pH was adjusted to 7 by adding a pH adjuster (sodium hydroxide).

Comparative Example 5 PP bumper and PU bumper test pieces were obtained in the same manner as in Example 1 except that the nonionic surfactant and the polyethylene polypropylene derivative foam suppressor were not used.

Comparative Example 6 Instead of the washing liquid prepared in Example 1, 50 g / liter of disodium phosphate, a nonionic surfactant (10 mol of ethylene oxide adduct of polyoxyethylene noniphenol ether, HLB13.5) A PP bumper and a PU bumper were prepared in the same manner as in Example 1 except that a cleaning liquid prepared from 1 g / liter and 0.5 g / liter of a polyoxyethylene polyoxypropylene higher alcohol-based foam suppressor (HLB5.5) was used. The test piece of was obtained.

Example 12 Using the PP bumper and PU bumper test pieces obtained in Examples 1 to 11 and Comparative Examples 1 to 6, the bumper surface performance was evaluated based on the evaluation method described in detail below. . The obtained results are shown in Table 1.

(1) Appearance evaluation method of coating By visual judgment, appearance abnormality is classified into three stages (good, partially defective,
The evaluation was non-uniform (occurrence of cissing).

(2) Primary adhesion evaluation method JIS was applied to the coating film surface of the test piece which was left indoors for 24 hours after coating.
-In accordance with K-5400, insert 11 parallel lines vertically and horizontally with a sharp cutter at 2 mm intervals, and cut a 2 mm square grid (1
(00 pieces) shaped cut scratches were produced. Then, a cellophane adhesive tape was adhered to the coating film surface of the test piece, peeled off at once, and the number of coating films remaining on the coating film surface without peeling together with the adhesive tape was counted and numerically evaluated.

(3) Secondary Adhesion Evaluation Method A test piece left to stand in a room for 24 hours after coating was immersed in deionized water at 40 ° C. for 10 days, and left in a room for another 24 hours, and then according to JIS-K-5400. 11 parallel lines were put vertically and horizontally by a sharp cutter at intervals of 2 mm to make a 2 mm square cross cut (100 pieces) -shaped cut scratches. A cellophane adhesive tape was attached to the coated surface and peeled off, and the number of cross-cut coating films remaining on the coated surface of the test piece was counted and numerically evaluated.

[0058]

[Table 1]

From Table 1, it was found that the cleaning method of the present invention does not adversely affect the performance of the bumper coated surface. On the other hand, when the cleaning conditions of the present invention are insufficient (including the conventional cleaning method), it is found that the performance of the bumper coated surface is adversely affected and sufficient cleaning performance is not exhibited.

[0060]

As described above, according to the present invention, when a polypropylene and / or polyurethane bumper is washed before coating with a specific acidic aqueous solution, no solvent is used and the washing step is short. Thus, it is possible to obtain an excellent effect on the coating performance and to obtain a cleaning method with a low impact on the environment.

Particularly, as a pre-coating cleaning method for the plastic bumper molded using zinc stearate as the internal mold release agent, it is possible to carry out cleaning in a short step without using any solvent.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location C11D 7:26) (72) Inventor Isamu Hara 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Katsumi Motojima 2 Takaracho, Kanagawa-ku, Kanagawa Prefecture Nissan Motor Co., Ltd. (72) In Sonor, Sonoko Sunami 4-chome, Minami-Shinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd., Tokyo Office (72) ) Inventor Yoshiki Yamane 4-1-115 Minami-Shinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo office

Claims (2)

[Claims] 1. A polypropylene and / or polyurethane bumper made of nonionic (a) mineral acid 0.1 to 100 g / liter, (b) fluorine compound 0.01 to 10 g / liter, and (c) HLB 12 to 16. Type surfactant, 0.1-10 g / liter, (d) polyethylene polypropylene derivative defoaming agent having HLB of 6 or less and having a mixing weight ratio to the above (c) of 0.1 to 2, and (e) sodium and / or A step of washing at 60 to 80 ° C with an acidic aqueous solution detergent containing an ammonium pH adjuster at 60 to 80 ° C, a step of washing the acidic aqueous solution washing solution with water, air blowing, and a step of drying at room temperature to 80 ° C are sequentially performed. A method for cleaning a plastic bumper, which is characterized by: 2. The method for cleaning a plastic bumper according to claim 1, wherein the polypropylene and / or polyurethane bumper is a molded product using zinc stearate as an internal mold release agent.